Abstract
The tobacco hornworm, Manduca sexta, undergoes several larval molts before transforming into a pupa and then an adult moth. Each molt culminates in ecdysis, when the old cuticle is shed. Prior to each larval ecdysis, the old cuticle is loosened by pre-ecdysis behavior, which consists of rhythmic compressions that are synchronous along the abdomen and on both body sides, and rhythmic retractions of the abdominal prolegs. Both pre-ecdysis and ecdysis behaviors are triggered by a peptide, eclosion hormone. The aim of the present study was to investigate the neural circuitry underlying larval preecdysis behavior. The pre-ecdysis motor pattern was recorded in isolated nerve cords from eclosion hormone-treated larvae, and the effects of connective transections and ionic manipulations were tested. Our results suggest that the larval pre-ecdysis compression motor pattern is coordinated and maintained by interneurons in the terminal abdominal ganglion that ascend the nerve cord without chemical synaptic relays; these interneurons make bilateral, probably monosynaptic, excitatory connections with identified pre-ecdysis motor neurons throughout the abdominal nerve cord. This model of the organization of the larval pre-ecdysis motor pattern should facilitate identification of the relevant interneurons, allowing future investigation of the neural basis of the developmental weakening of the pre-ecdysis motor pattern that accompanies the larval-pupal transformation.
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Abbreviations
- A3, A4...:
-
abdominal ganglia 3, 4...
- AT:
-
terminal abdominal ganglion
- ALE:
-
anterior lateral external muscle
- DN:
-
dorsal nerve
- DNA :
-
anterior branch of the dorsal nerve
- DNL :
-
lateral branch of the dorsal nerve
- DNP :
-
posterior branch of the dorsal nerve
- EH:
-
eclosion hormone
- TP:
-
tergopleural muscle
- VN:
-
ventral nerve
- VNA :
-
anterior branch of the ventral nerve
- VNL :
-
lateral branch of the ventral nerve
- VNP :
-
posterior branch of the ventral nerve
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Novicki, A., Weeks, J.C. Organization of the larval pre-ecdysis motor pattern in the tobacco hornworm, Manduca sexta . J Comp Physiol A 173, 151–162 (1993). https://doi.org/10.1007/BF00192974
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DOI: https://doi.org/10.1007/BF00192974